Honda HRX217HMA Owner's Manual page 51

SERVICING YOUR LAWN MOWER
Fuel Recommendations
Use unleaded gasoline with a pump octane rating of 86 or higher.
This engine is certified to operate on unleaded gasoline with a pump
octane rating of 86 or higher. Unleaded gasoline produces fewer
engine and spark plug deposits and extends exhaust system life.
Never use stale or contaminated gasoline or an oil/gasoline mixture.
Avoid getting dirt or water in the fuel tank.
Occasionally you may hear light "spark knock" or "pinging" (metallic
rapping noise) while operating under heavy loads. This is no cause for
concern.
If spark knock or pinging occurs at a steady engine speed, under
normal load, change brands of gasoline. If spark knock or pinging
persists, see an authorized Honda servicing dealer.
NOTICE
Running the engine with persistent spark knock or pinging can cause
engine damage.
This is considered misuse, and the Distributor's Limited Warranty
(page 75) does not cover parts damaged by misuse.
For oxygenated fuel information refer to page 67.
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